The invention relates to a method and apparatus for controlling an automatic transmission for a motor vehicle having at least one selection device by which the gears of the transmission can be manually shifted up and down in a manual mode, and an electronic control unit that predetermines a gear selection for controlling setting elements of the transmission. The electronic control unit predetermines the gear selection as a function of the signals of the selection device, shifting characteristics, and further input signals.
Such an apparatus is known to the applicant from its own patent application DE 10 2006 025 625 A1, for example. This known apparatus has a first selection device in the form of a selection lever, with which the gears P, R, N, D that can be set in automatic mode can be determined. Using a second selection device in the form of a steering wheel having two switches, the gears of the transmission can be manually shifted up or down, step by step, in manual mode. This known apparatus has an electronic transmission control unit that is usual in the case of automatic transmissions or automated manual transmissions.
In the known method, a first down-shift is undertaken, when at least the second selection device is activated into the manual down-shift position and the selection device is held in this down-shift position, by an electronic control device that controls the setting elements of the transmission as a function of the signals of the selection devices and further input signals. Subsequently, if the selection device is held in the down-shift position for a longer time, further down-shifts are performed sequentially, if a maximal permissible speed of rotation of the drive motor is not exceeded during each further down-shift.
For this purpose, the selection device is configured in such a manner that not only tapping but also holding of the selection device in a specific position can be detected. The detected position is reported to the control device, which is configured to evaluate the detected position, to undertake monitoring of the speed of rotation of the drive motor, and, in accordance with the method according to the invention, to cause the down-shifts to take place, if applicable also in a time-controlled manner.
These sequential multiple down-shifts require relatively long shifting times.
It is the object of the invention to provide an improved method and apparatus for controlling an automatic transmission with regard to faster driving dynamics desired by the driver.
This and other objects are achieved according to the invention, wherein the shifting characteristics for kick-down shifting for gear selection, in the sense of a kick-down simulation, are activated in the motor vehicle by the at least one selection device, by which the gears of the transmission can be manually shifted up and down in manual mode, and by an electronic control unit that predetermines a gear selection for controlling the setting elements of the transmission as a function of the signals of the selection device, of shifting characteristics, and of further input signals when the selection device is activated into the down-shift position that requests manual down-shifting and the selection device is held in this down-shift position for a predetermined period of time. The kick-down simulation can be maintained in a time-controlled or event-controlled manner.
The invention can be used both in a permanent manual mode and in a temporary manual mode. The permanent manual mode (M mode) can be activated by way of a selection lever, for example, when this is changed from a D position to an M position. The D position is usually assigned to an automatic mode, and the M position is assigned to a manual mode. The temporary manual mode permits manually triggered down-shifts or up-shifts, proceeding from the activated automatic mode, in other words even if the selection lever remains in the D position, for example if special down-shift and up-shift keys (e.g. switches or paddles on the steering wheel) are activated. This already corresponds to the state of the art.
The invention generally achieves very fast down-shift performance, if a down-shift key (e.g. the minus paddle already present in BMW vehicles with automatic transmissions) is activated for a longer period of time, by means of preconditioning of the gear selection into the shortest possible gear. In this connection, in contrast to actual activation of the kick-down switch on the gas pedal, no compulsory torque increase takes place.
This preconditioning of the gear selection is achieved, according to the invention, by way of simulation of a kick-down within the transmission control device, but only with reference to the selection of the shifting characteristics provided for kick-down. A torque increase in the drive machine (internal combustion engine or electric motor) does not necessarily take place. This kick-down simulation according to the invention is achieved with only one operating step, namely if the down-shift key (as an example of a second selection device) is activated for a longer period of time.
For example, in this connection, longer holding of the down-shift key in the down-shift position—in contrast to a short shifting command for only one down-shift—can be recognized by a timer-controlled evaluation. After this timer elapses, a trigger signal simulates a “kick-down=active” signal within the control device, independent of activation of the gas pedal and of the actual kick-down switch.
The shifting characteristics thereby selected for the usual kick-down shifts can thereupon preferably be maintained until the down-shift key is released or the down-shift position is departed from. However, other exit criteria from the kick-down simulation, such as a further time control, can also be defined.
Shifting in the sense of a shift request is initiated by way of the software-side linking of the “true” kick-down signal input of the control unit with this “kick-down=active” signal recognition simulated by the software, from the timer-controlled recognition of long pressing of a down-shift key; i.e. a gear selection takes place as a request and thereby independent of the possibilities of actual implementation in the transmission. The shortest possible gear that is permissible or possible in accordance with other general conditions (e.g. over-revving of the drive motor) is predetermined in accordance with the kick-down shifting characteristics.
The advantage of the invention lies in the simplicity of its implementation, because the kick-down gear selection thresholds are used for finding the gear, and therefore no separate further software-side thresholds (limit speeds of rotation, limit speeds, etc.) have to be used for the gear selection.
Fundamentally, the “kick-down=active” recognition signal simulated by the software would also be possible by way of representation by way of suitable hardware-side shifting.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.